Traditionally, card readers are associated with an access point to a system or building. In a physical access control system, card readers are commonly located at a door and each person who is authorized to enter the premises carries an access card that interacts with the readers. The access card can contain a semiconductor chip containing an EEPROM memory or a similar device (e.g., a radio-frequency identification (RFID) chip or an application-specific integrated circuit (ASIC) chip) that is programmed with a code number. The code number can be a single value or stored in multiple fields that correspond to, e.g., a serial number and a facility code to designate a building or series of buildings. Generally, the card is programmed by the card manufacturer before delivery to the systems integrator or user. The chip within the card is connected to an antenna, and the card transmits the number to the card reader through use of an electromagnetic induction signal.
The reader is typically no more than a pass-through device, where the reader routes messages to the control panel without addition or modification. The reader typically sends out an interrogating signal at 125 KHz to 134 KHz, known as Low Frequency (LF). Other frequencies are also used; for example, another frequency band known as HF operates at the singular frequency of 13.56 Mhz. The card is presented to the reader (e.g., by being placed in proximity to the reader), and the reader reads a message from the card. The reader is programmed to strip the message of its overhead structure, and reformat the message in a standardized data stream which the reader sends to a control panel. For example, the standardized format can be the so-called Wiegand code. The control panel may or may not recognize the card as belonging to the population of authorized entrants. If the card is recognized as authorized, the panel takes appropriate action to open the door which generally involves setting a relay that sends an electric current to activate a device at the door (e.g., a magnetic strike or lock).
FIG. 1 is a block diagram of a system 100 comprising a card access control reader 103 connected to a control panel 101, as illustrated in the art. The reader 103 is connected to the control panel 101 via connection 102 (e.g., Wiegand interface). A card 104 is presented to the reader 103 (e.g., by passing the card in close proximity to the reader, or touching the card to the reader) using an RFID signal 105, and the reader 103 receives a message from the card 104.